Generally, laminated multiple layer glass panels refer to a laminate comprised of a polymer sheet or interlayer sandwiched between two panes of glass. The laminated multiple layer glass panels are commonly utilized in architectural window applications, in the windows of motor vehicles, airplanes, trains and other modes of transporting people and goods, and in photovoltaic solar panels. The first two applications are commonly referred to as laminated safety glass. The main function of the interlayer in the laminated safety glass is to absorb energy resulting from impact or force applied to the glass, keep the layers of glass bonded even when the force is applied and the glass is broken, and prevent the glass from breaking up into sharp pieces. Additionally, the interlayer generally gives the glass a much higher sound insulation rating, reduces UV and/or IR light transmission, and enhances the aesthetic appeal of the associated window. In regards to the photovoltaic applications, the main function of the interlayer is to encapsulate the photovoltaic solar panels which are used to generate and supply electricity in commercial and residential applications.
The interlayer is generally produced by mixing a polymer resin such as poly(vinyl acetal) with one or more plasticizers and melt blending or melt processing the mix into a sheet by any applicable process or method known to one of skill in the art, including, but not limited to, extrusion. Other additional additives may optionally be added for various other purposes. After the interlayer sheet is formed, it is typically collected and rolled for transportation and storage and for later use in the multiple layer glass panels, as described below. Interlayer sheets of the appropriate size and thickness are sometimes cut, stacked and shipped in such stacks for later use in the multiple layer glass panels.
The following offers a simplified description of the manner in which multiple layer glass panels are generally produced in combination with the interlayers. First, at least one interlayer sheet, either monolithic or comprising several coextruded or prelaminated layers (“multilayer interlayers”), is placed between two substrates, such as glass panels, and any excess interlayer is trimmed from the edges, creating an assembly. It is not uncommon for multiple monolithic interlayer sheets to be placed within the two substrates creating a multiple layer glass panel with multiple monolithic interlayers. It is also not uncommon for multilayer interlayer sheets that comprise several coextruded or prelaminated layers, or multilayer interlayer sheets in combination with monolithic interlayer sheets to be placed within the two substrates creating a multiple layer glass panel with multilayer interlayers. Then, air is removed from the assembly by an applicable process or method known to one of skill in the art; e.g., through nip rollers, vacuum bag, vacuum ring, vacuum laminator, or another de-airing mechanism. Additionally, the interlayer is partially press-bonded to the substrates by any method known to one of ordinary skill in the art. In a last step, in order to form a final unitary structure, this preliminary bonding is rendered more permanent by a high temperature and pressure lamination process known to one of ordinary skill in the art such as, but not limited to, autoclaving.
A structural poly(vinyl acetal) interlayer, Saflex™ DG41 (a poly(vinyl butyral) polymer (“DG41”) having a weight average molecular weight (Mw) of about 170,000), is commercially available for applications in the architectural space. While the glass transition temperature (“Tg”) of DG41 is suitable for many architectural applications (˜46° C.), it would be desirable to raise the Tg of the interlayer to take advantage of a full range of applications it could have in the architectural space. Higher Tg products are desirable as they may be suitable for more demanding architectural applications that are exposed to consistently higher temperatures, especially those that require high modulus at higher ambient temperatures.
One methodology to increase the Tg of the poly(vinyl acetal) interlayer is to reduce the amount of plasticizer in the poly(vinyl acetal) resin. Reducing the amount of plasticizer, however, decreases the flowability of the polymer composition making processing quite difficult. DG41 is already difficult to process in extrusion compared to other more highly plasticized polymers owing to its lower level of plasticizer level of about 20 parts of plasticizer per hundred parts resin. The low plasticizer level in DG41 decreases its flowability, resulting in reduction in melt flowability and manifests itself as a large pressure drop between the head of the extruder or the melt pump to the back face of the die plate with a corresponding drop in extruder output or capacity. Although the processing of DG41 is difficult, it remains at an acceptable level. However, attempting to increase the Tg of the poly(vinyl acetal) interlayer by further dropping the amount of plasticizer may so decrease the flowability of the polymer composition so as to make its processing unacceptable.
Increasing the plasticizer level assists in improving the polymer flowability, thereby facilitating processing in the extruder manifesting itself as a lower pressure between the extruder head or melt pump to the back face of the die. However, increasing the plasticizer level also decreases the Tg of the interlayer.
It would be desirable to provide a poly(vinyl acetal) thermoplastic resin that has both an enhanced Tg and high E′ modulus (which is a measure of the layer's stiffness or rigidity), and that has good flowability. The increase in Tg cannot be accomplished by a mere drop in the amount of plasticizer since, as already mentioned, the processing conditions suffer through large pressure drops resulting in a loss in output capacity. It would also be desirable to provide the flexibility of not having to increase the thickness of the layers in order to achieve a higher interlayer rigidity.